[FEA] Support polars.Expr.str.find_many in cudf-polars

[brandon-b-miller]

Is your feature request related to a problem? Please describe.
Today on branch-25.08, we lack support for polars.Expr.str.find_many. Running the example from the docs yields:

import polars as pl
engine = pl.GPUEngine(raise_on_fail=True)

df = pl.DataFrame(
    {
        "values": ["discontent", "rhapsody"],
        "patterns": [
            ["winter", "disco", "onte", "discontent"],
            ["rhap", "ody", "coalesce"],
        ],
    }
).lazy()
df = df.select(pl.col("values").str.find_many("patterns"))


res = df.collect(engine=engine)
print(res)

NotImplementedError: find_many'

Describe the solution you'd like
I'd like the above code to be able to execute using the polars GPU backend. This API returns a list where the indices are the positons of the starting characters of all the found patterns. This seems to be a bit of a mix of cudf::strings::findall and cudf::strings::find_re, and is also blocked on being able to return a list[str] dtype.

Describe alternatives you've considered
N/A

Additional context
#16480

[davidwendt]

This too perhaps https://docs.rapids.ai/api/cudf/stable/pylibcudf/api_docs/strings/find_multiple/